In variable capacitive transducer or capacitive pressure sensors, capacitance varies with the pressure applied to the sensor and can be detected by an appropriate electronic circuitry. A typical capacitive pressure sensor is highly nonlinear. One example of a capacitance-pressure relation is
                              C          ⁡                      (            p            )                          =                              C            00                    +                      kC            0                    +                                    C              0                                      1              -                                                                    C                    0                                    κ                                ⁢                p                                              +                                    aC              0                                      1              -                                                                    C                    0                                                        b                    ⁢                                                                                  ⁢                    κ                                                  ⁢                p                                                                        (        1        )            
where C00, C0, and κ are independent statistical parameters of a capacitive pressure sensor. Parameters k, a, and b are constants for a given sensor type. The applied absolute pressure is p. FIG. 1 shows a capacitance vs. pressure characteristic with parameter values C00=0.65 pF, C0=3.25 pF, κ=4180 kPa*pF, k=0, a=0.808 and b=1.410.
In a pressure measurement system utilizing this kind of capacitive sensor, nonlinearity must be corrected to obtain an output signal proportional to pressure. In other words, the circuit must have some property which realizes the inverse function for the function presented in Equation 1 and FIG. 1. The solution of p from Equation 1 leads to a complex expression involving square root, hardly being feasible from the point of view of circuit design. In any case, a complicated electronic circuitry is required. Even if the capacitance-pressure relation were approximated by an equation simpler than Equation 1, it would still be difficult to design an electronic circuit which outputs signal p(C) when sensor capacitance is C.